1. Field of the Invention
The present invention relates to a clutch drum which is made of a metallic plate and which is formed by pressing in the peripheral wall portion thereof spline teeth which are engaged with clutch plates, as well as to a method of manufacturing the above-described clutch drum.
2. Description of Related Art
In manufacturing this kind of clutch drum, the following steps have conventionally been followed. Namely, a cup-shaped raw material made of a metallic plate is set by fitting it onto an external surface of a die which has peripheral tooth grooves or spaces corresponding to spline teeth. The peripheral wall of the cup-shaped raw material is pushed or urged by tooth-shaped punches which are disposed around the die and which can be radially moved back and forth. The spline teeth are thereby formed by pressing.
In order to improve the forming accuracy of the spline teeth, it is necessary to strongly press or urge the side or flank portions of the spline teeth to thereby reduce the roll over or shear drop in the corner portions at the tooth top.
However, in this case, the wall thickness of the tooth flank portions will be reduced and, consequently, the clutch drum is likely to be cracked from an open end of the clutch drum under the influence of the centrifugal force at the time of high-speed rotation. The strength of the clutch drum consequently decreases.
In view of the above-described points, the present invention has an object of providing a clutch drum made of a metallic plate which has an improved strength at the time of high-speed rotation.